A typical method for manufacturing mirror-surface wafers employed as raw material wafers for fabricating semiconductor devices will be explained below. First, a single-crystal semiconductor ingot is grown by the Czochralski method (CZ method) or the floating zone melting method (FZ method). Because the grown semiconductor ingot is distorted on the outer periphery thereof, the outer periphery of the semiconductor ingot is subsequently ground in a contour grinding process, e.g. with a cylindrical grinding tool, and the outer peripheral shape of the semiconductor ingot is adjusted. The ingot is then sliced with a wire saw or the like in a slicing process and machined to obtain disk-shaped wafers with a thickness of about 500-1000 μm, and the outer periphery of the wafers is then chamfered in a chamfering process.
Flattening is then conducted by lapping, followed by an etching process, then primary polishing, and secondary polishing. Mirror-surface wafers are then obtained by conducting epitaxial growth process on the wafer surface.
The above-described etching process is carried out for the purpose of removing processing-induced distortion that occurred in the previous processes, minute defects present on the front and rear surfaces of the wafers, and the matter adhered thereto. An etching apparatus is used for etching the front and rear surfaces of the wafers in the etching process. The conventional etching apparatus will be briefly described below with reference to FIG. 12. FIG. 12 is a longitudinal sectional view of the conventional etching apparatus, as viewed from the front surface thereof.
This etching apparatus mainly comprises an etching chamber 12 filled with an etching solution, a plurality of rods 16 for supporting and rotating a multiplicity of wafers 30, and a housing 10 accommodating the tank and the rods. A plurality of annular wafer support grooves 124 are provided equidistantly on the circumferential surface of the rods 16, and the outer peripheral sections of wafers 30 are fitted into the wafer support grooves 124 to hold the wafers 30. On the other hand, the rods 16 rotate about the central axis thereof.
With the etching apparatus of such configuration, if the inside of the etching chamber 12 is filled with an etching solution and the rods 16 are rotated, the wafers that are in contact by the outer periphery thereof with the rods 16 will also rotate. The etching solution located around the wafers 30 is stirred by the rotation of the wafers 30 and the front and rear surfaces of the wafers are etched. After such etching has been carried out for a prescribed time, the wafers 30 are taken out from the etching apparatus, thereby completing the wafer etching process.